1. Field of the Invention
The present invention relates to a plasma display device, and more particularly, to a plasma display device which maintains cooling efficiency of the device displaying in one position uniform with the cooling efficiency in another position when the plasma display device is rotated from the first position to the other.
2. Description of Related Art
Various flat display devices have been developed as substitutes for cathode ray tube (CRT) display devices. The flat display devices developed include, for example, liquid crystal display (LCD) devices, electroluminescence display (ELD) devices, field emission display (FED) devices, and plasma display panels (PDPs) which may also be referred to as plasma display devices.
The PDP displays an image using visible rays emitted when gas discharge is generated in a panel. A plurality of electrodes are formed on the panel of the PDP, and driving circuits for supplying driving signals to the electrodes are formed on printed circuit boards provided on a rear surface of the PDP.
A data driving unit, a scan driving unit, a sustain driving unit, a power supply unit, and a control circuit unit are typically separately formed on several printed circuit boards according to function or location.
Generally, the aforementioned driving units are separately formed on several printed circuit boards. The scan driving unit and the sustain driving unit may be formed on the same board. That is, the printed circuit boards include driving unit boards on which the data driving unit, the scan driving unit, and the sustain driving unit are formed, a board on which a power supply unit for supplying a voltage for generating driving signals is formed, and a board on which a control circuit unit for controlling the driving units and the power supply unit and processing external data is formed.
On the boards where the driving units are formed, at least one intelligent power module (IPM) separate from the power supply unit is mounted. The IPM converts a DC voltage supplied from the power supply unit into a signal voltage by controlling the driving unit. That is, the IPM converts the DC voltage into a voltage having a different level or inverts the polarity of the DC voltage to generate a signal voltage required for driving the PDP.
During operation, the IPM generates a large amount of heat in the PDP. This is because potentials of driving waveforms for driving the PDP are much higher and the number of the applied waveforms is much greater than those of the other display devices. When a subfield is divided into an address period, a reset period, and a sustain period, reset discharge, address discharge, and sustain discharge are generated during each period. The sustain discharge is generated up to a maximum of 128 times during one subfield and a magnitude of the signal voltage for generating each one discharge is several tens of volts to several hundreds of volts. The address discharge is generated by applying address signals having different polarities to two electrodes, and a difference between address signal voltages applied to the two electrodes reaches several hundreds of volts. Because such high voltage driving signals are applied several tens of times in one second, the IPM for generating the driving signals is designed to endure such a load.
When heating elements, or heat generating elements, such as the IPM can not efficiently dissipate the heat they generate, the heating elements deteriorate, are damaged, or the signals are distorted and thus the PDP can not operate normally. Accordingly, to dissipate the heat generated at the heating elements, a cooling means such as a heat sink is attached to one side of the IPM.
FIGS. 1A and 1B illustrate a conventional heat dissipator or heat dissipating element used in a conventional PDP 1. FIG. 1A illustrates arrangement of a conventional heat dissipator 2 and a corresponding air flow. FIG. 1B illustrates the heat dissipator 2 and a corresponding air flow when the PDP 1 is rotated by 90 degree.
The conventional PDP 1 is said to be mounted in a horizontal position when a horizontal side is longer than its vertical side. Conversely, the PDP is said to be mounted in a vertical position when the vertical side of the PDP is longer than its horizontal side. FIG. 1A schematically illustrates the arrangement of the heat dissipator 2 of the PDP 1 and does not illustrate other structures of the PDP 1. The heat dissipator 2 includes wings 2a and plate 2b. When the PDP 1 is mounted as shown in FIG. 1A, the heat dissipator 2 mounted in a heating portion, such as the IPM, is such that the wings 2a extend in a vertical direction. Air flows between the wings 2a of the heat dissipator 2 to cool the heat dissipator 2. This structure can increase the cooling efficiency using air convection, and is made in consideration of the convective circulation that occurs due to air density difference. In contrast, when the wings 2a extend in the horizontal direction, the cooling efficiency is remarkably reduced.
As shown in FIG. 1B, when the wings 2a of the heat dissipator 2 extend perpendicular to the air flow direction, all but the lowest wing have very low contact ratios with the flowing air and thus it is difficult to efficiently dissipate the heat.
PDP products that can be used in both horizontal and vertical positions, shown respectively in FIGS. 1A and 1B, have recently come into the market. Accordingly, a conventional PDP, which is normally used in the horizontal position, can also be used in the vertical position by rotating the PDP by 90 degree. A PDP which can display in both the horizontal and the vertical positions is known as a PDP having a pivot function.
However, the PDPs having the pivot function also have the cooling problem described with reference to FIGS. 1A and 1B. That is, because the heat dissipator mounted on the printed circuit board is fixed to the heating portion and the wings are fixed in one direction, when the PDP is rotated using the pivot function, the wings of the fixed heat dissipator extend perpendicular to the air convection direction. Therefore, when the conventional PDP 1 uses the pivot function, the cooling efficiency is remarkably reduced in one of the vertical or horizontal positions and thus the elements frequently malfunction or are damaged.